1. Field of the Invention
The invention relates to electro-optic conversion modules, and particularly to the use of fiducial markings on such printed boards in such modules for verification of printing alignment, fabrication accuracy, and quality control of printed electrical connectors fabricated on such boards.
2. Description of the Related Art
Optical data transmission networks provide high capacity signal transmission without many of the physical limitations of electrical cables. Fiber-optic transceivers used in such networks convert electrical signals into optical signals and vice versa at the interface of a fiber-optic cable and an electronic network unit, such as a computer or communications system.
To extend the application of the fiber optic transceiver for mass-produced, low-cost computer and communications devices, it is desirable for the individual components to be economical to fabricate, and thus the electrical connect to be simple and reliable at the same time. The typical hardware design of these low-cost transceivers provides the use of a printed circuit board that terminate on one side with a cut out pin edge or a contact array forming a multi-pin electrical connector, which may be implemented on one or both sides of the board. With such a contact array, the circuit board can be directly plugged into a mating electrical receptacle on the back end of the chassis of a host computer. The cut out connector may also be elongated, and sized to be able to extend through an open slot in the back face of the computer chassis so that connection may be made to a receptacle mounted inside the chassis on a mother board of the computer.
A number of industry standards have been defined to integrate some of these electrical connector design considerations into opto-electronic transceiver modules. For example, the XENPAK standard (see www.xenpak.org) describes an advantageous opto-electronic transceiver module package with a cut out printed circuit board electrical connector.
Like any lithographically printed circuit board, mask alignment and routing introduce variations from board to board that present issues of reliability and quality control, especially for high density pin configuration.
Prior to the present invention, there has not been a reliable process to ensure quality control in parallel optical module with a cut-out printed pin array electrical connector. Thus, it is desired to have a fiducial mark associated with the board design for the pin out or electrical contact array for making the electrical connection from the board which can be quickly and easily visually checked by quality assurance personnel in a production environment to determine if the routed board meets specification.